Blades for gas turbines



c. M. TUNSTALL ET AL 25830357 BLADES FOR GAS TURBINES April 15, 1958 Filed May 22, 1955 United States Paten't'Q 2,830,357 BLADES FOR GAS TURBINES Application May 22, 1956, Serial No. 586,601 Claims priority, application Great Britain May 27, 1955 13 Claims. (Cl. 29--156.8)

This invention relates to a method of making metal blades for use in gas turbine rotors, the said blades being of the kind, hereinafter referred to as the kind described, comprising a Working portion of aerofoil section provided with longitudinally extending internal passages for conveyance of a cooling fluid, a root portion with abutment shoulders, through which centrifugal forces acting on the blade when in service are resisted, and a platform part between the working portion and the root portion, the, working portion and the root portion extending on opposite sides of the platform part.

One method of making a blade of the kind described is to machine the blade from a blade blank having at least a lengthwise part of the same shape and dimensions in cross-section as the platform part of the blade, the blade blank also having internal passages running longitudinally through the blank, the passages being of such size and so disposed in the blank as to form the required passages in the blade which is formedfrom the blank.

A convenient method of forming such a blank is by extrusion, but it will be appreciated that other methods may be used.

In cases in which the internal passages in the blank would break through or approach too closely the abutment shoulders of the root portion of a blade to be machined from the blank however, the method outlined above for making a blade of the kind described is unacceptable, and the object of the present invention is to supplement the method previously outlined in a manner such as to render it acceptable from the point of view discussed.

According to the'present invention there is provided a method of making a blade of the kind described from a blade blank having at least a lengthwise extending part at one end of substantially the same shape and dimensions in cross-section as the platform part of the blade to. be formed from the blank, the blade blank also having internal passages running longitudinally through the blank, the passages being of such a size and so disposed in the blank as to form the required passages in the blade which is to be formed from the blank, which method comprises forming the root portion of the blade by machining anopen ended slot in said lengthwise extending part of the blank from said one end of the blank to a depth not exceeding the length of the root portion of the blade which is to be formed from the blank, forging the blank to press the prongs thus formed into contact with one another over at least a part of their length from said one end of the blank, and then machining a portion of the blank at said one end of the blank to produce the root portion of the blade, the size, form and disposition of said slot being such that after the forging operation said portion of the blank can be machined to the required root form without any of said passages breaking through any load carrying abutment shoulder of the root.

According to a feature of the present invention the 2 ment shoulders of the root extending parallel with th plane of contact of the prongs, in which case the size, form and disposition of the slot are also chosen such that after the forging operation said portion of the blank can be machined to the required root form without the walls of the slot breaking through any load carrying abutment shoulder of the root. Alternatively however, according to another feature of the present invention, the rootportion of the blade may be formed with the abutment shoulders of the root extending substantially perpendicular to the plane of contact of the prongs so that'the said plane intersects the sides of the root provided with the abutment shoulders.

According to another feature of the present invention said blade blank may be an extruded bar which has a cross-section of substantially the same shape and dimensions as the platform part of the blade to be formed from the blank and a length substantially equal to the length of the blade to be formed from the blank, and said method may further comprise machining another portion of the blank to produce the aerofoil cross-sectioned working portion of the blade.

According to another feature of the present invention said slot may be so formed as to be bounded in part by flat surfaces which meet the end surface of the blade blank at said one endof the blank in parallel lines which bound on said end surface an area which'contains all the openings to said internal passages at said one end of the blank, so that when said prongs are pressed into contact with one another as aforesaid, said internal passages are closed at said one end ofthe blank. 7 I

Usually, the blade blank has more'than two internal passages, and the passages are so disposed in the blank as to be on an are which follows the curve of the convex and concave surfaces of the aerofoil cross-sectioned working portions of the blade to be formed from the blank.

In this case, according to another feature of the present invention, said slot may be formed so that one of said parallel lines is the common tangent to the two of said internal passage openings which will be most widely spaced in the chordal direction of the blade Which is to be formed from the blank on the side thereof nearest the thrust face of the blade, and the other of said parallel lines is that tangent to the one of said internal passage openings which tangent and passage openings are spaced furthest from said common tangent.

It will be appreciated however that where suflicient metal is available outside the passages said parallel lines may be more widely spaced, and that Where it is not necessary for the passages to be closed at the end of the blank the parallel lines may be more narrowly spaced.

According to yet another feature of the invention said slot may be formed with said flat bounding surfaces parallel to one another and with said surfaces joined by a curved boundary surface at the base of the slot, and said prongs may be pressed into contact with one another over part only of the extent of said flat bounding surfaces from said one end of the blank thereby leaving a passage of tear-drop shaped crosssection extending transroot portion of the blade may be formed with the abutversely of and in communication with all said internal passages.

Alternatively however according to yet another feature of the invention said slot may be formed with said flat bounding surfaces inclined relatively to one another to give a Vsectioned slot of a depth not greater than, the

length of the root portion of the blade which is fobe formed from the blank.

Two methods in accordance with the present invention of making a blade of the kind described having a fir -t'ree-"type"of root 'will now be described merely'b'y way which will benearest'the back surface of' the blade.

of example with reference to the accompanying drawings whereof:

Figure 1 is a plan view of a finished blade looking from the tip of the working portion of the blade towards the platform part of the blade,

Figure 2 is a longitudinal section corresponding to the line 3-3 in Figure 1 through the root portion of a blade blank after an initial stage of forming the root according to the first method which is about to be described,

Fi'gufe 3 is a similar section through the finished root, and

Figures 4 and 5 show two stages in the formation of the root portion of a blade according to the second method which will hereinafter be described.

The blade shown in Figure 1 comprises a platform part 1 of parallelogram shape in planview. From one face of the platform part projects a working portion 2 of aerofoil section and from the other face a root portion '3, not visible in Figure 1 but shown in Figure 3, comprislug a fir tree root 4 with abutment shoulders 5 and an extended root portinpart'6 between the last of the abutment shoulders and'the platform part. Extending longitudinally through the working portion 2 and the platform part 1 are four parallel passages 7, 8, 9 and 10 for conveyance of' a cooling fluid, such cooling fluid being admitted into the passages through four ports 70, 8a, 9a and 10a in the extended part 6 of the root portion:

As may be seen from Figure l the passages 7, 8,- 9, and 10 lie on an are which follows the curve of the convex and concave surfaces of the working portion 2 of the blade.

A blade of this kind is conveniently made from a blade blank in the form of a length of extruded bar substantially equal in length to the finished blade and 5.

having a cross-section corresponding in shape and dimensions, apart from a machining allowance, to the plan view of the platform part 1, theextrusion being formed, by methods which do not form part of the present invention, with longitudinally extending internal passages so that the blade blank has such passages running through it, the passages being of such size and so disposed in the blank as to form the passages '7, 8, 9 and 10 of the blade which is to be made from the blank. As will be seen from the dotted line 11 in Figure 3 the passage 8 would, if the root portion 3 were machined upon an end portion of the unpretreated blank, break through the first of the abutment shoulders on the left hand side of the root portion. and would pass undesirably close to the other abutment shoulders on that side of the root portion, so much so that the root portion would be seriously weakened. To a lesser extent the other passages 7, 9 and 10 would also weaken the root portion.

To overcome this objection an open ended slot 12 is cut in the end surface 30 of the end portion of the blank from which the root portion 3 is to be formed. The slot is cut to a depth equal to the length of the root portion 3 and so as to be bounded on opposite 7 sides by flat parallel surfaces 13 and 14, which extend parallel with the passages 7 to 10. As will be seen from Figure 1 the surfaces 13 and 14 meet the end surface in parallel lines 31, 32 respectively which bound on the surface 30 an area which contains all the openings to the passages 7, 8,9 and 10 in the surface. Of the lines 31, 32 the line 32 is the common tangent to the openings in the surface 30 to the passages 7 and 10, which passages are the passages spaced most widely in the chordal direction of the blade which is to be formed from the blank, on, the side of the passages7 and 11 which tangent and passage are spaced furthest from the line 32, that is to say line 31 is, in the present example,

the tangent to thatjside of the opening tothe passage 8 In the present example, since the surfaces 13and14 are parallel to the passages 7 to 10 it will be appreciated that the surfaces 13 and 14 are also tangent surfaces to the passages 7 and 10, and 8 respectively. Thus the slot 12 in effect cuts out only the metal of the end portion of the blank which isto form the root portion which contains the passages 7 to 10. At the base of the slot the surfaces 13 and 14 are joined by a cylindrical boundary surface 15.

By cutting the slot 12 two prongs 16 and 17 are formed at the end of the blade blank, and these are now forged into contact with one another as shown by the dotted lines in Figure 2 over part only of the extent of the surfaces 13 and 14 from the end surface 30 of the blank, a rod ofhard material preferably being inserted in the bottom of the slot to maintain the radius 15. The two prongs contact one another over a flat surface 18 which is arranged to lie in a radial plane through the centre of gravity of the finished blade, and the root portion is itself formed ashereinafter described so as to lie symmetrically on each side of the surface 18. To achieve the correct disposition of the surface 18 with the configuration shown the prong 17 has to be pressed inwardly rather more than the prong 16. The forged part of the blank is now machined to form the root portion 3 as shown in Figure 3 and the other end portion of the blank, on the opposite side of the platform-forming part 1, is machined to form the aerofoil sectioned working portion 2 of the blade. If required, a shroud can also be provided at the tip of the blade.

On completion of this machining a blade is obtained having longitudinal passages 7, 8, 9 and 10 running into a passage 19 of tear-drop shape extending transversely through the extended root part 6. If desired, this passage may be used as an inlet for the cooling fluid, one end being possibly closed by a plate brazed to the end of the root, or both ends may be closed, and inlet ports 7a, 8a, 9a and 10a drilled through into the passage 19 from the sides of the extended root part 6.

In the second method the blade root portion 3 is formed by cutting the slot 12 in V section instead of with parallel sides, the apex of the V being located below the platformforming part of the blade blank and ending in a stress relieving drilling 20. Like the surfaces 13 and 14 of the parallel sided slot shown in Figure 2, thesurfaces 21 and 22 of the V slot meet the end surface 30 of the blank in parallel lines which may be disposed in relation to the openings to the passages 7 to 10 in the surface 30 as previously described with reference to the lines 31 and 32. In the present example they are however more Widely spaced than this as may be seen from Figure 4. In any case, when the prongs 16 and 17 thus formed are forged into contact with one another along the surfaces 21 and 22, as shown by the dotted lines in Figure 4, the passages 7 to 10 are completely closed at the forged end of the blank. .After machining the forged end portion of the blank to form the root portion 3 as shown in Figure 5,

the drilling 20 may 'be opened out and used as a cooling fluid supply passage or header passage, one or both endsof the drilling possibly being plugged.

7 Whilst the minimum requirement is that the internal passages such as 7 to 10 should not break through any of the abutmentshoulders, such as 5, of the root portion,

it is desirable soto dimension and position the slot such to the manufacture of blades of the kind described which have other than fir tree type roots, and the blade blanks may be made by forging instead of by extrusion, in which case the working portion of the blade may be either rough forged for finishing by machining or may be precision forged so as to require only polishing.

Where, either in an extruded or a forged blank, the

internal passages such as 7 to 10 extend over so much of an arc in the working portion of the blade that a slot in the root would have to be of impracticably great width to contain them, the root portion may be subjected to a preliminary forging operation to flatten the arc of distribution of the passages sufiiciently to reduce to an acceptable value the width of the slot which has to be cut.

Whilst in the embodiments shown the root is formed with the abutment shoulders extending parallel to the common plane of contact of the prongs formed on the blank by the slotting process, the root could alternatively be formed with the abutment shoulders extending substantially perpendicular to the said common plane so that the said plane intersects the sides of the root provided with the abutment shoulders.

In this case the root might be designed to fit into a circumferential slot in a turbine rotor disc the abutment shoulders lying along large radius arcs centered on the axis of the rotor of which the blade is to form a part. In this case also, the platform part would be curved and centered on said axis.

We claim:

1. In a method of making a blade of the kind described from a blade blank having at least a lengthwise extending part at one end of substantially the same shape and dimensions in cross-section as the platform part of the blade to be formed from the blank, the blade blank also having internal passages running longitudinally through the blank, the passages being of such a size and so disposed in the blank as to form the required passages in the blade which is to be formed from the blank, forming the root portion of the blade by slotting said lengthwise extending part of the blank from said one end of the blank to a depth not exceeding the length of the root portion of the blade which is to be formed from the blank so as to form a pair of prongs on the blank while at the same time removing at least some of the metal of the blank between said passages, forging the blank to press the prongs into contact with one another over at least a part of their length from said one end of the blank, and then machining a portion of the blank at said one end of the blank to produce the root portion of the blade, the size, form and disposition of said slot being such that after the forging operation said portion of the blank can be machined to the required root form without any of said passages breaking through any load carrying abutment shoulder of the root.

2. A method as claimed in claim 1, in which the root portion of the blade is formed with the abutment shoulders of the root extending parallel with the plane of contact of the prongs, the size, form and disposition of said slot also being such that after the forging operation said portion of the blank can be machined to the required root form without the walls of the slot breaking through any load carrying abutment shoulder of the root.

3. A method as claimed in claim 1, in which the root portion of the blade is formed with the abutment shoulders of the root extending substantially perpendicular to the plane of contact of the prongs so that said plane intersects the sides of the root provided with abutment shoulders.

4. A method as claimed in claim 1, wherein said slot is so formed as to be bounded in part by flat surfaces which meet the end surface of the blade blank at said one end of the blank in parallel lines which bound on said end surface an area which contains all the openings to said internal passages at said one end of the blank, so that when said prongs are pressed into contact with one another as aforesaid, said internal passages are closed at said one end of the blank.

5. A method as claimed in claim 4, wherein said blade blank has more than two internal passages, and said passages are so disposed in the blank as to be on an are which follows the curve of the convex and concave surfaces of the working portion of the blade to be formed from the blank, and said slot is formed so that one of said parallel lines is the common tangent to the two of said internal passage openings which will be most Widely spaced in the chordal direction of the blade which is to be formed from the blank on the side thereof nearest the thrust face of the blade, and the other of said parallel lines is that tangent to the one of said internal passage openings which tangent and passage openings are spaced furthest from said common tangent.

6. A method as claimed in claim 4, wherein said slot is formed with said flat bounding surfaces parallel to one another and with said surfaces joined by a curved boundary surface at the base of the slot, and wherein said prongs are pressed into contact with one another over part only of the extent of said fiat bounding surfaces from said one end of the blank thereby leaving a passage of tear-drop shaped cross-section extending transversely of and in communication with all said internal passages.

7. A method as claimed in claim 6, further comprising closing one end of said transverse passage so as to leave a single opening in the blade root in communication with said internal passages.

8. A method as claimed in claim 6, further comprising closing each end of said transverse passage and then forming one or more inlet ports in the blade root which inlet ports communicate with said transverse passage.

9. A method as claimed in claim 4, wherein said slot is formed with said flat bounding surfaces inclined relatively to one another to give a V-sectioned slot of a depth not greater than the length of the root portion of the blade which is to be formed from the blank.

10. A method as claimed in claim 9, further comprising in part forming said slot by drilling to form a stress relieving drilling at the apex thereof.

11. A method as claimed in claim 10, wherein said stress relieving drilling intersects at least one of said internal passages, and the method further comprises, after forming said root portion, opening out at least part of the drilling for use as an inlet to said one of said internal passages.

12. A method as claimed in claim 4 wherein said prongs;

are pressed into contact with one another over a flat surface which lies in the plane of symmetry of the root portion of the blade to be formed from the blank.

13. A method as claimed in claim 4, further comprising subjecting said lengthwise extending part of the blank at said one end of the blank to a preliminary forging operation before machining said slot in order to flatten any are of distribution of said internal passages to reduce the width required for said slot.

References Cited in the file of this patent UNITED STATES PATENTS 2,431,249 Heppner Nov. 18, 1947 2,613,058 Atkinson Oct. 7, 1952 2,656,146 Sollinger Oct. 20, 1953 2,684,831 Grantham July 27, 1954 2,699,917 Colwell Jan. 18, 1955 

